Naa'imur Zakariyah Rahman, 20, allegedly thought he was just days away from inflicting "lethal violence with blade and explosion" before his arrest last November. But his plan was uncovered by an MI5 operative, who posed as a senior Isis official in Syria, the Old Bailey heard.

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Before his arrest prevented it, he was, he believed, just days away from his objective, which was no less than a suicide attack, by blade and explosion, on Downing Street and, if he could, upon the Prime Minister Theresa May herself.

Prosecutor Mark Heywood QC

The next day, jurors heard he said: "My objective is to take out my target. Nothing less than the death of the leaders of Parliament."

Rahman is charged with preparing terrorist acts by conducting reconnaissance, recording a pledge of allegiance, and delivering a rucksack and jacket to be fitted with explosives.

Prosecutor Mark Heywood QC said: "His settled conclusion was that lethal violence here, directed at the very heart of the United Kingdom government, was the only effective way to pursue his intentions.

"Before his arrest prevented it, he was, he believed, just days away from his objective, which was no less than a suicide attack, by blade and explosion, on Downing Street and, if he could, upon the Prime Minister Theresa May herself."

Jurors heard Houses of Parliament was a target (Image: GETTY )

The defendant, of Finchley, north London, is also charged with helping his friend Mohammad Aqib Imran, 22, to prepare terrorist acts.

He allegedly recorded a sponsorship video for Imran to join IS in Syria.

Mr Heywood said the men knew each other well, and shared the "warped ideology" of Isis.

Rahman's uncle had joined ISIS in Syria and allegedly encouraged his nephew to attack the UK before he was killed in a drone strike, jurors heard.

Mr Heywood said Rahman's focus was on attack planning in the UK (Image: GETTY )

By September last year, the defendants had allegedly met someone online who they believed would provide useful contacts.

Mr Heywood said Rahman's focus was on attack planning in the UK.

He said: "The evidence shows in detail his developing fervour as he first assembled his plan, carried out reconnaissance and perfected his ideas and then acquired the means to execute it.

"At the last he took back his own coat and his own rucksack both modified with improvised explosive devices, so that he could achieve his settled aim of a full frontal assault on the gates and then the door of Number 10.

"In this he expected to die. But he also hoped for personal reward beyond death and, in doing so, to cause death and great fear in a place and to people symbolic of the country itself."

On Imran's plans, Mr Heywood said: "He elected to travel and set about assembling money, acquiring a fake passport, engaging in research and otherwise equipping himself with the information and means to travel aboard for violence for terrorist purposes.

Rahman has denied two counts of preparing terrorist acts.

Imran, of Sparkbrook, Birmingham, has pleaded not guilty to preparing terrorist acts abroad and possessing a terrorist document on his Kindle entitled How To Survive In The West - A Mujahid's Guide 2015.